1. Field of the Invention
The present invention relates to a reducer of an electric power-assisted steering apparatus. More specifically, the present invention relates to a reducer of an electric power-assisted steering apparatus in which a worm shaft and a motor shaft are connected to each other such that, when a forward/reverse rotation is performed, vibration and noise transferred to the worm shaft and motor shaft are absorbed, and rattle noise and vibration are reduced while preventing a slip from occurring between the worm shaft and the motor shaft, thereby improving a driver's steering feeling.
2. Description of the Prior Art
FIG. 1 is a view illustrating a configuration of a conventional electric power-assisted steering apparatus. As illustrated in FIG. 1, an electric power-assisted steering apparatus 100 includes a steering wheel 102 disposed at a driver seat, a steering shaft 106 connected thereto, a steering column 130 configured to allow the steering shaft to be fixed to a vehicle body, a rack and pinion mechanism 110 including a rack gear and a pinion gear configured to convert a torque input from the steering shaft 106 into a rectilinear movement, and a rack bar 112 provided with a tie rod 122 and a knuckle arm 124 at each end thereof.
The steering column 130 includes a steering shaft 106 connected to the steering wheel 102 to be rotated together with the steering wheel 102, and, at the other side, connected to a pinion shaft 108 via a pair of universal joints 104. In addition, the pinion shaft 108 is connected to the rack bar 112 through the rack and pinion mechanism 110, and the opposite ends of the rack bar 112 are connected to vehicle wheels 126 through the tie rods 122 and the knuckle arms 124, respectively.
An auxiliary power mechanism 140 includes: a torque sensor 142 configured to sense a torque that is applied to the steering wheel 102 by the driver and to output an electric signal that is proportional to the sensed torque; an electronic control unit 144 configured to generate a control signal based on the electric signal transferred from the torque sensor 142; a motor 146 configured to generate an auxiliary power based on the control signal transferred from the electronic control unit 144; and a reducer 150 including a worm 152 and a worm wheel 156 in order to deliver the auxiliary power generated by the motor 146 to the steering shaft 106.
Accordingly, the electric power-assisted steering apparatus is configured such that a torque generated by the rotation of the steering wheel 102 is delivered to the rack bar 112 via the rack and pinion mechanism 110, and the auxiliary power generated by the motor 146 according to the generated torque is delivered to the rack bar 112. That is, the torque generated by the rotation of the steering wheel 102 and the auxiliary power generated by the motor 146 are combined with each other so as to cause the rack bar 112 to move in an axial direction.
FIG. 2 is a cross-sectional view illustrating a reducer of a conventional electric power-assisted steering apparatus. As illustrated in FIG. 2, the reducer 150 is provided with a worm shaft 254 that is formed with a worm 152, and worm shaft bearings 257 are provided at the opposite ends of the worm shaft 254 so as to support the worm shaft 254. In order to prevent the worm shaft bearing 257 from moving away in the axial direction of the worm shaft 254, a plug bolt 210 is fastened between a damping coupler 240 and the worm shaft bearing 257, and the plug bolt 210 is fixed by the plug nut 220.
The worm shaft 254 has a structure in which the worm shaft 254 is connected with the motor 146 via the damping coupler 240 such that the worm shaft 254 is rotated by the driving of the motor 146.
In addition, the worm wheel 156 is provided at one side of the outer diameter of the worm 152 to mesh with the worm 152 formed on the worm shaft 254. The worm wheel 156 has a structure to be mounted on the steering shaft 106 configured to deliver the torque of the steering wheel 102 (see FIG. 1) operated by the driver such that the torque of the worm shaft 254 applied by the driving of the motor 146 is delivered to the steering shaft 106.
The worm 152, the worm wheel 156, etc. run within a gear housing 260, and the motor 146 is provided at a side of the gear housing 260 to provide a driving force to the worm shaft 254. The gear housing 260 and the motor 146 are coupled to each other by a motor cover 230 with a bolt 250.
The reducer of the electric power-assisted steering apparatus configured as described above is configured to control the driving of the motor by an electronic control unit provided in a vehicle depending on a running condition of the vehicle, and to cause the torque of the worm shaft applied by the driving of the motor to be delivered to the steering shaft in addition to the torque of the steering wheel operated by the driver such that the driver's steering and driving conditions can be maintained smoothly and stably.
The above-described reducer of the conventional electric power-assisted steering apparatus has a problem in that, when the worm shaft and the motor shaft are connected to perform a forward/reverse rotation, vibration and noise are generated in the worm shaft and the motor shaft.
In addition, there is a problem in that, as the forward rotation and the reverse rotation are repeated, a slip occurs on the worm shaft and the motor shaft so that an unpleasant feeling may be caused to the driver due to rattle noise and vibration.